Recent content on Segflow
I had a 4 GiB file that’s almost entirely zeros, exactly one non-zero int64 is hiding at offset Size - 8 (the last aligned slot). The task: find that offset, as fast as possible, in Go on Linux. It’s a deliberately silly problem. There’s no parsing, no indexing, no cleverness on the algorithm side. The only thing it measures is how much data we can pull through a CPU per second.…
Don’t get me wrong – Oh My Zsh is an excellent product. It’s well-maintained, feature-rich, and has helped millions of developers enhance their shell experience. But here’s the thing: you don’t need it to have a great zsh experience . When I recently set up a new workstation, I decided to skip Oh My Zsh entirely and configure zsh manually. The result? A lightweight, fast,…
I argued earlier that a function’s signature should never lie , and then that errors are values only if you treat them like values . Both posts circled the same question at different scales: what is this code for? This one closes the loop at the package level. The short version: if your package is named utils , you don’t have an answer.
Last time I argued that a function’s signature should never lie . The error return is the most lied-about part of every Go signature I read. It gets logged, swallowed, repackaged, panicked on, and printed back to the user as internal error: internal error: internal error . Three habits keep it honest.
A function I once shipped looked like this: func Process ( data [] byte ) error Innocent. You give it bytes, it returns an error. What more do you need? Plenty, as it turned out. Process also wrote a file to /tmp , posted the same bytes to a webhook, and stashed a copy in a package-level global so the next call could “diff against the last one”. None of that was in the signature. None…
A small file-serving service of mine slowed to a crawl one afternoon after a “harmless” middleware change. CPU on the server box doubled, throughput roughly halved. The diff was a single line: instead of handing a *os.File to io.Copy , somebody had wrapped it in a tiny logging reader to count bytes. That one wrap quietly turned off sendfile(2) . This post is about that fast path: what…
I had a hot loop I could not get any faster. Plain for i := 0; i < n; i++ , two slice reads, one add, return. On paper that is three or four x86 instructions per iteration. In practice it was running at about half the throughput I expected, and perf kept pointing at the same two lines. When I finally dumped the assembly, the answer was sitting right there: a CMPQ followed by a conditional jump to…
A pipeline has backpressure when the consumer can make the producer slow down, or refuse the work, or both. A bigger buffer does neither. It just defers the same problem, with more memory held hostage in the meantime. The two get confused a lot, and the difference shows up unmistakably in the tail latency numbers, so this post does the comparison directly. When load exceeds capacity you have three…
The CLI was fast. I had benchmarked it on my laptop, on a fresh clone of the repo, and it finished in well under a second. Then a coworker pointed it at a real monorepo, the kind with 30,000 files spread across a few thousand directories, and the thing crawled. Same code, same machine class, just more files. The user-visible work had not changed. The wall clock had. This is the story of the half…
A while back I had a hot loop that profiled like a heap-allocation machine gun. pprof blamed runtime.mallocgc . The code looked innocent. The fix turned out to be a one-line signature change, and the compiler had been quietly screaming at me about it the whole time via -gcflags=-m . This post is the second half of a tour I started in My journey optimizing the Go Compiler and continued in What…
A few months ago my team had to kill a feature. Nothing dramatic; a half-finished onboarding flow product had quietly stopped believing in. The ticket said “remove the new welcome wizard.” I estimated two days. It took three weeks. The wizard itself was about 400 lines. The reason it took three weeks is that those 400 lines had grown roots. A flag on the user record. A column in the…
I had been telling people for months that Go can “trivially” hold a million idle TCP connections. The runtime uses epoll, goroutines are cheap, what could go wrong. Then a colleague asked me to actually do it, and I realised I had never tried. So I sat down with my laptop, a fresh net.Listen , and a client that just wants to open a lot of sockets. The first wall I hit was 1024 file…
After my map-lookup contribution to the Go compiler back in April, I kept poking the toolchain whenever a benchmark surprised me. Last week it surprised me again, and the lesson is short enough to fit in one post: Go inlines aggressively, but not infinitely, and the shape of your function matters more than its length. The story starts with a three-line helper that I was sure the compiler would…
At EDGE we write a lot of Go, and we love it for various reasons, one of them being speed. One day I got into a situation where I need to assign an int to a variable based on another string value. Sounds easy right? well yes, but this particular use case awakened the beast in me and made me think what’s the best way to do it. The journey finished by me contributing to the language compiler…
In this challenge, we are given a service IP and PORT, to which we can connect using netcat or any similar tool. We are also provided with an ELF file.
Below, you will find the full exploit for PlaidCTF pwn200 task. The full write-up will follow.
In this article I will share with you the solution to Secure Login challenge presented at Acebear CTF , this task was worth 900 points. Even though I did not manage to solve the challenge on time, I still enjoyed it a lot.
In this challenge, we are given a service IP and PORT, to which we can connect using netcat or any similar tool. We are also provided with a tar file that contains the service binary and some .so modules.
Recently I decided to start playing CTFs again, and since I needed some training before playing a real one, I decided to take a look at some recent CTFs in CTFtime.org . And then I found this crypto task with no write-up for it yet, and that’s why I jumped into it :)